Leonardo’s Mountain of Clams and the Diet of Worms (48 page)

But the more 1 ponder the subject,
the more I conclude that we should just try to know sloths as
they
perceive and record the world—and not just scan their repertoires for items that resonate with us, or bring us pleasure (including the sublime delight of a good outcome in the outhouse!). And yet, to really know, I need those sixty seconds
within
a
Bradypus
brain—and no power on earth can supply this gift and tool. So I ponder
the riddles of ordinary human walking seen as Keystone Kop freneticism, or of reaching for a leaf at t’ai-chi speed as another creature’s perception of average pacing. So near into that skull of a distant mammalian relative; so far to know directly.

For my second Costa Rican favorite, I turned to the carrion-feeding raptors, particularly the turkey vulture. I united these birds with the maximally
disparate sloths in my mind because both made me wonder so powerfully about “different worlds” in the heads of animals with lifestyles so starkly in contrast with our own choices and proclivities—the only world we can know directly. But I then discovered another connection quite unknown to me at the time. Both these creatures elicited maximal contempt from the greatest arbiter of historical taste—Georges
Buffon. I have already quoted Buffon’s deprecations of sloths. Now consider his opinion of vultures:

Buffon also tells us that we can easily distinguish vultures from eagles by the naked head and neck of the nasty carrion feeders versus the full feathering of the noble hunters. If this aristocratic French naturalist had known the supposed adaptive value of the vulture’s naked head, he would undoubtedly
have demoted these birds even further in his estimation—for we now remember Buffon mostly for his celebrated motto
“le style c’est l’homme même”
(the style is the man himself). Vultures plunge their entire head deep into rotting corpses, and a conventional mat of feathers would soon become dangerously fouled, while gore does not adhere to the smooth and naked skin. To cite a standard source (Leslie
Brown and Dean Amadon’s
Eagles, Hawks, and Falcons of the World
): “Without this denudation, the head feathers would become smeared and matted with gore and infection might occur.” (I have little sympathy for adaptationist scenarios in the “just-so story” mode, but this particular tale makes good sense to me, especially since the Old and New World vultures are not closely related by genealogy,
but have independently evolved this highly localized loss of feathers—apparently for the same functional reason.)

Little about these birds could possibly be judged as pleasant in human terms. Of the turkey vulture, my Costa Rican source of observation, Buffon concluded in an adjectival frenzy: “They are voracious, cowardly, disgusting, odious and, as with wolves, just as noxious during their
lives as they are useless after their death.” Consider the grandest of New World vultures, the great (and nearly extinct) California Condor, with maximal wingspan among all the world’s flying birds. I don’t wish to compromise the noble efforts now under way to save this magnificent species (for adherence to human ethical standards could scarcely be more irrelevant in our judgment of other animals),
but descriptions of feeding condors can scarcely inspire any visceral affection.

In the standard source on condor behavior, written in the early 1950s before the population had declined so precipitously, Carl B. Koford describes how a group of condors rips and struggles so vigorously at a carcass that the whole complex (of feeding birds and dead food source) slides slowly downhill:

In our current climate of emphasis upon “family values,” I won’t dwell upon details
of their manner of feeding. Suffice to say that the hides of sheep, deer, and cattle (the major sources of larger carcasses) are hard to penetrate—and that condors therefore begin by ripping away at natural orifices, and sticking their smooth heads into the opening bounty.

But I would still give (almost) anything for sixty seconds inside a turkey vulture’s head. What does their world look like,
as they circle silently above a carcass? What attracts them? What is their aesthetic? Does rot and corruption truly appeal—and, if so, the more the better, or only up to a certain point? Would I, the homunculus in the vulture’s brain, view (and smell) a dead cow on the plains as a human explorer might regard a pot of gold at the rainbow’s end, or an oasis in the desert?

As these questions emerged
in Costa Rica, several thousand miles from my library, I did not realize that an old and substantial literature had developed on this very subject—or at least on the strictly limited and operational way that humans can approach such questions by probing from our restricted position outside the bird’s own conceptual world. In particular, naturalists have long wondered and argued about how vultures
find their prey.

This old issue immediately raises two questions that both set the puzzle and complexify the answer. First, birds, in general, are preeminently visual animals, particularly so for the raptors (eagles, hawks, and their relatives) that stand in close genealogical proximity to some vultures. But carrion might be found better by smell than by sight. Do vultures therefore use a most
unbirdlike sense of smell to find their food? Second, as mentioned before, “vulture” is a functional term for large, carrion-feeding birds that have converged upon a set of common features from different genealogical roots. If we discover that one species can’t smell at all, we cannot conclude that another species (with a different evolutionary ancestry) might not use olfaction above all other senses.

The Old World vultures do, apparently, rely entirely upon sight. They take no notice of the most odoriferous parcel of deliciously rotting meat unless they can see the food. But some New World vultures do use smell as a primary sense. Debate has long centered upon the species I saw in Costa Rica, the turkey vulture
Cathartes aura.

The argument goes back at least to Audubon, who, in 1826, read
a technical paper before the Natural History Society of Edinburgh titled “Account of the habits of the turkey buzzard, particularly with the view of exploding the opinion generally entertained of its extraordinary power of smelling.” Audubon interpreted his ambiguous experiments as indicating that vultures could not smell, and located prey only with a keen sense of vision. He may have been correct
for the species he studied—not the turkey vulture, as he thought and misidentified, but the black vulture,
Coragyps.
The issue therefore remained open for my Costa Rican species.

As criticism of Audubon mounted, his friend, the eminent American naturalist John Bachman, performed a second set of experiments, supposedly to confirm Audubon’s conclusion. He even gathered a group of learned and respectable
citizens to observe his work and sign a document of assent (shades of Joseph Smith and official witnesses to the Mormon tablets).

Charles Darwin, as a young man in South America on the
Beagle
, took up the subject and, as usual, both asked the key question in the most fruitful way, and got the answer basically right. He did a crude experiment on the Andean condor
(Vultur gryphus)
and concluded
that this species does not smell. Darwin wrote:

But Darwin recognized that other species might smell, and he mentioned that evidence for the turkey vulture favored olfaction as an important sense:

(I might
add that Darwin also developed quite a fondness for Andean condors, despite their dubious lifestyle in human terms. He ended his discussion of this species by writing: “When the condors are wheeling in a flock round and round any spot, their flight is beautiful . . . It is truly wonderful . . . to see so great a bird, hour after hour, without any apparent exertion, wheeling and gliding over mountain
and river.”)

The issue of olfaction in turkey vultures was not conclusively solved until 1964, when Kenneth E. Stager presented overwhelming evidence, based on years of clever and careful experimentation, that
Cathartes aura
does indeed rely upon a keen sense of smell to find carrion. Turkey vultures will often make an initial identification by sight (though first clues can also be olfactory).
They then circle the carcass far above and in a wide arc until they catch a sniff downwind. The famous circle (our conventional icon for vultures) then shortens considerably in radius as the birds home in by odor before descending for the feast.

Ironically, Stager discovered that previous researchers often misread the evidence for olfaction because they assumed “the more putrid the better”—and
therefore tested birds with truly rotten meat. In fact, turkey vultures prefer food only slightly rotten and will reject highly putrid flesh if any alternative exists (or unless severe hunger demands compromise with usual standards). Stager writes: “
Cathartes
shows a preference for food that is relatively fresh rather than putrid. If food is in short supply in a given area, the turkey vulture
will feed on carrion that is well advanced in putrefaction. Tests . . . indicated that captive
Cathartes
showed a decided preference for recently dead, newly hatched chicks, rather than for putrefied carrion.”

I am grateful for all this good information, but I would so prefer my unobtainable minute in a turkey vulture’s brain, particularly at the first sight or whiff of a good dead meal on the
plains below.

Such conjectures inevitably bring up the contentious theme of animal “consciousness.” J confess that I find this subject, as usually debated, both tedious and utterly fruitless as a dispute about subjective
words
pursued by people who mistakenly think that they are arguing about important and resolvable
things.
If I ask “does a dog have consciousness,” the endless and passionate
arguments that ensue usually reduce to different definitions of this confusing word, rather than focusing upon interesting and empirically resolvable questions about what dogs can and don’t do. (I also admit, of course—for this essay takes the point as its major theme—that many questions raised by this fascinating topic do treat the genuine (things rather than words] but unknowable issue of a dog’s
internal state of mind.) Whether or not a dog “thinks” or “has consciousness” depends upon a chosen definition. Some people won’t grant “consciousness” to any creature that can’t abstract a general concept—truth or religion, for example—from particulars and then apply the apparatus of formal logic to make inferences even further away from starting points. Others confer “consciousness” upon creatures
that recognize kin and remember places of previous danger or pleasure. By the first criterion, dogs don’t; by the second, they do. But dogs remain dogs, feeling what they feel without regard to our chosen labels.

In the context of Costa Rica, and international efforts to preserve biodiversity, this issue assumes centrality because the classical argument for why a supposedly decent and moral creature
like
Homo sapiens
can mistreat and even extirpate other species rests upon an extreme position in a continuum. The Cartesian tradition, formulated explicitly in the seventeenth century, but developed in “folk” and other versions throughout human history no doubt, holds that other animals are little more than unfeeling machines, with only humans enjoying “consciousness,” however defined. Under
extreme versions of this theory, even the overt pain and suffering of other mammals (so palpable to us in the most visceral way because the vocal and facial expressions of such close evolutionary relatives match our own reactions to the same stimuli) only record an automatic response with no internal representation in feeling—because other animals have no consciousness. Thus, taking the argument further,
we might worry about extinction for other reasons, but not for any aggregate pain or distress in the requisite killing.